Electron ionization mass spectral analysis of novel O ‐aryl O ‐ethyl 2‐chloroethylphosphonates

Abstract

Electron ionization mass spectral analysis of novel O-aryl O-ethyl 2-chloroethylphosphonatesA number of electron ionization mass spectral (EIMS) investigations have been reported 1 -8 for organophosphonates, apart from a review 9 of the mass spectrometry of organophosphorus compounds. Generally two kinds of rearrangements are observed for organophosphonates: (i) a single hydrogen transfer due to McLafferty rearrangement and (ii) a double hydrogen transfer. 10 Some pyridyl-2-and pyridyl-4-phosphonates have been reported 11 to show both of these types of rearrangements. In the spectra of Oethyl O-alkyl methanephosphonates, only double hydrogen transfer was observed and not the McLafferty rearrangement. 12 In its sulfur analogues, i.e. O-ethyl S-alkyl methanophosphonothioates, the ratio of the abundances of the two fragments corresponding to the two rearrangements varied depending upon the chain length and branching of the S-alkyl group.Recently, we have synthesized a series of O-aryl O-ethyl 2chloroethyl phosphonates (1-12) and evaluated their fungitoxicity 13 and nematotoxicity. 14 As part of the programme, we report here the results of the EIMS analysis of the synthesized phosphonates (Table 1). Replacement of the aryl moiety by a heterocyclic moiety is known to increase the insecticidal activity of phosphonates. 15 With this in mind, two heteroaryl analogues (13 and 14) were also synthesized and their mass spectra were recorded. Although 13 agreed with the fragmentation pattern of the phosphonates 1-12, the phosphonate 14 showed a different behaviour.The phosphonates 1-14 were synthesized by the reaction of 2-chloroethylphosphonyl dichloride first with ethanol and then with the respective phenols/thiols in the presence of a base. 13 Gas chromatography/mass spectrometry (GC/MS) was carried out on a Fisons Instruments TRIO-1000 at temperatures from 45 to 300°C at a rate of 16°C min 1 with helium as the carrier gas at a rate of 2 ml min 1 (HP 1 column, injector temperature 220°C, interface temperature 250°C).The mass spectral analysis of the 12 O-aryl O-ethyl 2chloroethylphosphonates 1-12 and the two O-heteroaryl O-ethyl 2-chloroethylphosphonates 13 and 14 revealed that the fragmentation pattern of 14 is different from that of 1-13.EIMS fragmentations of the 12 O-aryl O-ethyl 2-chloroethylphosphonates 1-12 and the O-heteroaryl O-ethyl 2-chloroethylphosphonate 13 differing only in the aryl moiety can be grouped into two categories. One includes the common fragments present in all the compounds independent of the aryl/heteroaryl moiety and the other includes the common fragments present in all the compounds retaining the aryl/heteroaryl moiety and consequently mass shifted. The structural variation of the phosphonates, the m/z values of their fragments with relative abundances and their GC retention times t R are listed in Table 1.